On the role of wind driven ocean dynamics in tropical Atlantic variability
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The response of the tropical Atlantic Ocean to wind stress forcing on seasonal and interannual time scales is examined using an ocean data assimilation product from the Geophysical Fluid Dynamics Laboratory (GFDL), and an ocean general circulation model which incorporates a three dimensional flux correction technique to correct biases of the mean state of the ocean. On a seasonal time scale, we investigated the impact of the annual migration of the ITCZ on the exchange pathways of the northern tropical Atlantic. The results indicate that seasonal variation of the zonal slope of the thermal ridge along the boundary between the north equatorial countercurrent and north equatorial current in response to changes in the ITCZ controls, to a large extent, the amount of water participating in the equatorial circulation. These changes can be explained in terms of a simple dynamical model where local Ekman pumping dominates thermocline variation in the western part of the basin, and Rossby wave adjustment comes into play in the eastern basin. On an interannual time scale, we examined the upper heat budget of the equatorial Atlantic in order to identify the key mechanisms by which wind-driven ocean dynamics control SST variability during the onset and peak phases of the Atlantic zonal mode. It is found that, in contrast with Pacific ENSO, both Bjerknes and Ekman feedbacks act together to force the zonal mode, although their relative importance and dominance depend on season and location.
Da Silva, Meyre Pereira (2003). On the role of wind driven ocean dynamics in tropical Atlantic variability. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from